Tire tread with variable-width recesses

ABSTRACT

A pneumatic tire is provided with a tread whose recessed portions have a width that decreases from the surface of the tread towards the axis of the tire. The recessed portions have a greater variation of width as a function of depth at the edges than in the central part of the tread.

United States Patent Boileau TIRE TREAD WITH VARIABLE-WIDTH RECESSESInventor: Jacques Boileau, Clermont-Ferrand,

France Assignee: Compagnie Generale des Etablissements Michelin raisonsociale Michelin & Cie, Clermont-Ferrand, Puy-de-Dome, France Filed:Jan. 19, 1971 -Appl. No.: 107,650

Foreign Application Priority Data Jan. 21, 1970 France .....7o2204 U.S.c1 4152/209. Int. Cl ..B60c 11/06 Field of Search ..l52/209 [451 Dec.26, 1972 [56] References Cited UNITED STATES PATENTS 3,512,567 5/1970Verdier ..152/209 2,779,378 1/1957 Robertson 1 52/209 PrimaryExaminer-James B. Marbert Attorney-Brumbaugh, Graves, Donohue & Raymond[57] ABSTRACT A pneumatic tire is provided with a tread whose recessedportions have a width that decreases from the surface of the treadtowards the axis of the tire. The recessed'portions have a greatervariation of width as a function of depth at the edges than in thecentral part of the tread.

4 Claims, 6 Drawing Figures PATENTEU [IEB26 I972 3.707.177

sum 1 or 2 INVENTOR. JACQUES BOILEAU his ATTORNEYS PATENTEDnmzs m2 sum 2BF 2 INVENTOR. JACQUES BOILEAU his ATTORNEYS BACKGROUND OF THE INVENTIONThis invention relates to pneumatic tires and, more particularly, tonovel and highly-effective treads for new or recapped tires,particularly tires of the radial type.

Treads have proportions of recessed areas as compared to the total treadarea that depend on the use (winter or summer driving, for example) forwhich they are intended. Generally the proportion of recessed areas,hereinafter called the cutout percentage, is about 40 percent for awinter tire but may be as low as about 25 percent for a summer tire inthe case of automobile tires.

For various reasons, the cutout percentage in winter tires does notexceed about 40 percent, even through the adherence of a winter tire isrelated to a very high cutout percentage.

First, the use of very high cutout percentages leads to a reduction inthe strength of the relief elements.

Second, the higher the cutout percentage the more uncomfortable drivingon roads that are free of snow or ice becomes, even to the point that itis necessary to change tires in order to travel on normal roads.

SUMMARY OF THE INVENTION An object of the invention is to remedy themost serious shortcomings of conventional snow tires and, in particular,to provide a snow tire that has a very high cutout percentage but thatcan be driven comfortably in other than winter conditions, especially asthe wear of the tire increases. v The foregoing and other objects areattained in accordance with the invention by the provision of a snowtire with a tread whose recessed portions have a width that decreasesfrom the surface of the tread towards the axis of the tire. The tire ischaracterized in that the recessed portions have a greater variation ofwidth as a function of depth at the edges than in the central part ofthetread.

In one representative embodiment, the ratio of the widths of therecessed portions at the surface of the new tread and 2 mm from thebottom of the recesses is greater than 3 at the edges of the tread andis between 1 and 3 in the central portion of the tread. The side regionsof the tread each occupy a width of about 1/5 to 1/6 of the total widthof the tread, the central portion extending over the remaining 3/5 to asof the width.

As a result of this structure, one can employ on the surface of thetread of the new tire a cutout percentage equal to or greater than 40percent but not exceeding 75 percent. Since the relief elements have arelatively wide base, they are less fragile, particularly at the edges,and have less of a tendency to squeal and to hammer the ground.Furthermore, the wear of the tread of the tire results in a reduction ofthe cutout percentage and a change of its characteristics towards thoseof a summer tire having a cutout percentage of close to 30 percent. Thetire can thus be used in summer. In accordance with the invention, thisreduction in the cutout percentage is greater in the side re gions ofthe tread. The variation in width of the recessed portions can takeplace either continuously and progressively or, on the other hand,intermittently in individual steps. The inclination of the sidewalls ofthe recessed parts may be constant, or, on the contrary, it may varylocally.

In another embodiment of the invention, the recessed portions and therelief elements are of larger dimensions on the edges than at the centerof the tread, which favors the adherence of the winter tire. Preferably,the recessed portions and the relief elements have a general orientationthat is generally transverse at the edges and longitudinal or oblique(i.e., other than generally transverse) in the central portion of thetread.

BRIEF DESCRIPTION OF THE DRAWING An understanding of other aspects ofthe invention can be gained from a consideration of the followingdetailed description of preferred embodiments thereof, in conjunctionwith the appended figures of the drawing, wherein:

FIG. 1 is a plan view of a sector of approximately 20 of a tread inaccordance with the invention for a tire of size -380 or 6.50-15;

FIG. 2 is a view in meridian half section taken along the line 2-2 ofFIG. 1 and looking in the direction of the arrows;

FIG. 3 is a view in section through an edge portion taken along the line3-3 of FIG. 1, parallel to the longitudinal axis X-X and looking in thedirection of the arrows;

FIG. 4 is a plan view of a sector of about 20 of another tread inaccordance with the invention for a tire ofsize -355 or 7.75-14;

FIG. 5 is a view in meridian half section taken along the line 5-5 ofFIG. 4 and looking in the direction of the arrows; and

FIG. 6 is a view in section through an edge portion taken along the line6-6 of FIG. 4, parallel to the longitudinal axis Y--Y and looking in thedirection of the arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a portion of atread l'comprising in its central part 2 a plurality of isolated,oblique, right-sloping relief elements 3 inclined 40 towards the rightand left-sloping relief elements 4 inclined 40 toward the left, theinclination of these elements being indicated with respect to thelongitudinal axis X-X of the tread 1. The central relief elements 3 and4 are separated from each other by recessed portions such as 5, 6, 7 and8. Edge relief elements 10 are heavier than the central relief elements3 and 4 and are separated from the central relief elements 3 and 4 byrecessed portions 13, l4,and 15. Each edge relief element 10 is orientedin a generally transverse direction and has an oblique segment 18 and atransverse segment 19; they are separated from each other by recessedportions 20 oriented in a generally transverse direction.

FIG. 2, which is a meridian half section along the line 2-2 of the treadof the preceding figure, shows that the recessed portions 5, 6 and 7 (aswell as 8 and 14, which are not shown) have a stepwise variation inwidth 23. The level 0 corresponds to the new tire, the level -1, whichis intermediate the levels 0 and 2, corresponds to the steps 23; and thelevel --2 corresponds to the solid portion of the tread (total wear).The steps 23 impart to the relief elements 3 or 4 massive bases despitea cutout percentage of 64 percent at the level (new tire) in the centralregion. In accordance with the invention, the ratio of the respectivewidths of the recessed portions 5, 6 and 7, shown in FIG. 2, and 8 and14 (not shown in FIG. 2) at the surface of the tread (level 0) to thewidths of the same recessed portions 2 mm from the bottom thereof isabout 1.6. At the level 1, the ratio is lower, and the cutout percentagedrops to about 48 percent.

FIG. 3 shows a partial cross-section along the line 33 parallel to thelongitudinal axis X-X of the tread. The segments 19 of the reliefelements have at their center transverse slots 30-extending to the level2. The relief portions 20 have two narrow transverse slots 31 and a widecentral channel 33 also extending up to the level 2. However, theserecessed portions 20 extend only to the level 1 aside from the slots 31and 33.

The central channel 33 is in communication with the recessed portions ofthe central zone 2 of the tread 1 due to the recessed portions 14. Ineach edge region,

the cutout percentage is 47 percent at level 0 and l6 percent atlevel 1. The ratio of the widths of the recessed portions 20 measuredparallel to the straight line 3-3 at level 0 to the width of the sameportions at 2 mm from the bottom of the recesses 31 and 33 is about 3.2.Moreover, the walls of the recesses have an inclination of 2 to 5.

- Cuts such as 34 and 35, the walls of which touch, are intended to makethe ends of the relief elements 3, 4 and 10 flexible and extend to thelevel 2.

Thus, in accordance with the invention, the variation of the percentageof cutout between the levels 0 and 1, on the one hand, and 0 to 2, onthe other hand, is much greater in the side regions.

As FIG. 1 shows, anti-skid studs 26 can be inserted in accordance withthe invention in the relief elements 4 of the central region 2 of thetread in addition to the studs located in the edge relief elements 10.This studding can extend without drawback to all the relief elements 3and 4 of the central region 2.

In the embodiment of FIG. 4 the tread portion 40 has in the centralregion 41 three longitudinal ribs 42, 43 and 44. The equatorial rib 43is spaced from the central ribs 42 and 44 by grooves 45 and 46; thecentral ribs 42 and 44 are spaced from the edge ribs 47 and 48 bygrooves 49 and 50.

As shown in FIGS. 5 and 6, the variations in width of the recesses alsotake place in steps. As in the case of FIGS. 1, 2 and 3, the levels ofthe new tread and those of the recesses have been designated by 0, 1 and2.

In this embodiment of the invention, the cutout percentage is 60 percentfor the tread at level 0 and at level -1 40 percent for the centralportion and 15 percent for the two edges of the tread.

The ratios of the widths of the recessed portions at level 0 to thewidths thereof at 2 mm from the bottom of the recesses are 1.6 for thegrooves 45 and 46, 2 for the grooves 49 and 50 and 5 for the slots 51provided on the edges of the tread.

The grooves 49 and 50 have steps 52 at level 1. Similarly, the grooves45 and 46 have steps 54 (FIGS. 4 and 5). The marginal grooves 51 areoriented transversely and have slots 56 that extend to level 2, whilethe steps 57, 58 and 59 are flush with the intermediate level The edgeanti-skid studding at 60 and 61 is supplemented by a studding at 62 ofthe central ribs 42 and 44 having reinforced bases in accordance withthe invention; it can be extended without drawback to the equatorial rib43. I

The flexing cuts such as 70, 71 in the ribs 42, 43 and 44 and such as 72and 73 in the ribs 47 and 48 of the edges extend down to level 2 of thetread.

Many other embodiments of the invention will readily occur to thoseskilled in the art upon reading this disclosure. Forwexample, onecan,.without exceeding the scope of the invention, replace recesseswhose width varies discontinuously by recesses whose width variescontinuously as a function of depth. Moreover, in the case ofdiscontinuous variation, the change in width can take place in anynumber of steps and can be different from one region of the tread toanother. Accordingly, the invention is to be construed as including allthe embodiments thereof within the scope of the appended claims.

I claim:

1. A pneumatic tire initially suitable for use as a snow tire and, as itwears, for use as a summer tire, said tire comprising a tread, saidtread having distributed thereover relief elements defining recesses,the bottoms of said recesses having substantially the same width in allportions of said tread, and the tops of said recesses havingsubstantially greater width near the edges of said tread than in thecenter of said tread, whereby the decrease in groove width at the treadsurface as said tread wears is not uniform over the area of said treadbut substantially greater near the edges of said tread than in thecenter of said tread.

2. A tire according to claim 1 wherein the ratio of the width of saidrecesses at the tread surface when new to the width of said recesses 2mm from the bottom thereof exceeds 3 at the edges of the tread and iswithin the range of 1 to 3 in the central portion of the tread.

3. A tire according to claim 1 wherein the tread when new has a cutoutpercentage at the surface thereof within the range of 40 to 75 percent,said cutout percentage decreasing to about 30 percent as the treadwears.

4. A tire according to claim 1 wherein said relief elements and saidrecesses have a generally transverse orientation at said edges and anorientation other than generally transverse in said central portion.

1. A pneumatic tire initially suitable for use as a snow tire and, as itwears, for use as a summer tire, said tire comprising a tread, saidtread having distributed thereover relief elements defIning recesses,the bottoms of said recesses having substantially the same width in allportions of said tread, and the tops of said recesses havingsubstantially greater width near the edges of said tread than in thecenter of said tread, whereby the decrease in groove width at the treadsurface as said tread wears is not uniform over the area of said treadbut substantially greater near the edges of said tread than in thecenter of said tread.
 2. A tire according to claim 1 wherein the ratioof the width of said recesses at the tread surface when new to the widthof said recesses 2 mm from the bottom thereof exceeds 3 at the edges ofthe tread and is within the range of 1 to 3 in the central portion ofthe tread.
 3. A tire according to claim 1 wherein the tread when new hasa cutout percentage at the surface thereof within the range of 40 to 75percent, said cutout percentage decreasing to about 30 percent as thetread wears.
 4. A tire according to claim 1 wherein said relief elementsand said recesses have a generally transverse orientation at said edgesand an orientation other than generally transverse in said centralportion.